1. Field of the Invention
The invention relates to a polymer material, and in particular to a water-vapor permeable film and a textile comprising the same.
2. Description of the Related Art
Thermoplastic polyurethane (TPU) is a soft elastomeric resin with high tensile strength, wearproof, low temperature resistance, and strong adhesion. The polyurethane, also meeting environmental requirements due to decomposability, with no use of solvent during processing, has been widely applied in textiles and ready-made clothes. In film processing, a thin (<20 μm) and uniform (±15%) film can be obtained using a blown film method.
When polyurethane film is rolled or pulled, film blocking may easily occur due to high surface friction force thereof, resulting in film breakage. Conventional addition methods are employed to solve the problem. Additive quantity, however, is large, increasing costs. Also, die-build-up may occur during fabrication due to water absorption of the polyurethane.
Thus, development of a water-vapor permeable film fabrication method with prevention of film blocking and die-build-up is desirable.
Current water-vapor permeable polyurethane fabrication methods mainly comprise adding hydrophilic functional groups to polymer structure. Other accessory methods such as adding absorbent powders, creating pores, forming cross-linking structure, or adding aromatic compounds also increase water-vapor permeability or film strength. There are many patents related to water-vapor permeable polyurethane, mainly comprising use of additives or film modification by back-end processing. Few, however, relate to film composition.
U.S. Pat. No. 6,790,926 discloses a water vapor permeable polyurethane, and fabrication and application thereof. The polyurethane comprises a polyether-polyol containing high weight percentage of ethylene oxide (comprising polyethylene glycol (PEG) and 4,4-methylene bisphenyl diisocyanate (MDI)), a small molecule chain extender, and an araliphatic diol. Addition of the araliphatic diol containing benzene structure increases resin strength and reduces adhesion between films.
US 2004/092,696 discloses a polyurethane comprising a polyether intermediate containing ethylene oxide (containing two terminal hydroxyl functional groups) and a chain extender such as araliphatic diol. The polyurethane provides high melting temperature, high tensile strength, and anti-static electricity. This patent also discloses a textile combined with the polyurethane, capable of elongation, high water vapor permeability, thermal resistance, and processability.
US 2003/195,293 discloses an aqueous and water vapor permeable polyurethane comprising a polyol containing ethylene oxide. No emulsifying agent or amine neutralizer is required during water dispersion due to formation of the hydrophilic ethylene oxide chains, preventing pollution from solvents or small molecule vaporized substances. Wound dressing materials or textiles combined therewith also provide high water vapor permeability. Additionally, film strength is improved by addition of other polymer materials.
JP 2000/220,076 discloses a solvent-based polyurethane containing at least 20 wt % ethylene oxide. To avoid over-concentration of ethylene oxide in soft segment, a diol chain extender containing ethylene oxide is further added to increase ethylene oxide content in hard segment. Thus, water vapor permeable groups are uniformly distributed in the polyurethane, increasing film strength.
DE 4,442,380 discloses a polyurethane comprising one or more polyether polyurethanes, one of which is a water vapor permeable polyethylene glycol polyurethane, and other polyurethanes selected by strength requirements. Ethylene oxide content and mixing ratio among polyether polyurethanes are defined. Polyester polyurethanes, however, are not suitable for use due to lower water vapor permeability.
DE 4,339,475 discloses a polyurethane having 35˜60 wt % ethylene oxide comprising polyether-polyol. To facilitate coating, melting viscosity less than 70 is required. The small molecule chain extender comprises ether-diol and ester-diol. Large molecule polyester-polyol, however, is not used.
U.S. Pat. No. 5,254,641 discloses a water vapor permeable polyurethane film comprising a polyurethane containing polyethylene glycol (PEG) with a hardness of 75A˜92A and 5˜20 wt % polyether-amide or polyether-ester. Film strength can be effectively improved by addition of the polyether-amide or polyether-ester.
U.S. Pat. No. 5,283,112 discloses a polyurethane comprising a hydrophilic polyethylene glycol (PEG) and a hydrophobic polydimethyl siloxane (PDMS). During fabrication, phase separation is more complete due to different hydrophilicity of components, resulting in stronger film. Also, softness of polyurethane and its adhesion to substrate can be improved by addition of PDMS.
EP 335,276 discloses a water vapor permeable non-yellowing polyurethane comprising an aliphatic or cyclo-aliphatic diisocyanate, a polyether-polyol containing ethylene oxide, and a diol. The soft polyurethane having optimal physical modulus can be obtained, suitable for use in extrusion processing.
GB 2,087,909 discloses a solvent-based polyurethane. A short-chain diol is first mixed with exceeding duisocyanate to form a pre-polymer. Next, a polyethylene glycol (PEG) is added thereto. A polyurethane containing 25˜40 wt % polyethylene glycol is thus formed. Film strength is improved by addition of the longer hard segment pre-polymer comprising the diol and diisocyante.
WO 9,000,969, WO 9,000,180, and GB 2,157,703 disclose a two-component or pre-polymer-type polyurethane comprising a polyether-polyol such as polyethylene glycol (PEG), a chain extender, and a cross-linking reagent. The resulting polyurethane has exceeding NCO and provides low viscosity. Additionally, film strength is increased by formation of cross-linking structure.